In systems responsive to handwritten symbols, such as signature verification systems or character recognition systems, it is often desirable to "normalize" an entered symbol before the symbol is submitted to subsequent processing steps. Normalization may include rotations, changes in size and/or translations to different positions. For example, in a signature verification system in which a signature to be verified is compared with one or more stored model signatures, or where parameters representing salient characteristics of a signature to be verified are compared with corresponding parameters derived from one or more model signatures, it is typically necessary to normalize both the model signatures and the signatures to be verified to remove differences unrelated to shape.
In some methods of recognizing handwritten symbols, a separate normalizing step is not necessary. We disclose such a method in our copending application Ser. No. 07/857,198 filed Mar. 24, 1992. In accordance with the invention described in such application, an unknown symbol handwritten on a digitizing tablet is compared with symbols in a predefined "alphabet" or library of model symbols and the closest match chosen. Recognition is independent of the size, position or orientation of the symbols. The comparison involves calculating a correlation factor from scalar products of vectors representing coordinate samples from the unknown symbol and the model symbols. In such method, the normalizing function is inherent in the comparison procedure.
However, for those applications where normalization is required, such as some methods of symbol recognition and/or signature verification, it is desirable to have a fast, straightforward method of performing such normalization.